Drill



April 10, 1956 J. F. JOY 2,741,461

DRILL Filed Sept. 7, 1950 6 Sheets-Sheet l E Q' 3b 230 34' I I I I s4JnsepllflJby A TTORNEY April 10, 1956 .1. F. JOY 2,741,461

DRILL Filed Sept. 7, 1950 6 Sheets-Shae; 3

NVENTOR.' JosepllFJby B QF A rramvsy J. F. JOY

April 10, 1956 DRILL 6 Sheets-Sheet 5 Filed Sept. 7, 1950 J. F. JOY

April 10, 1956 DRILL 6 Sheets-Sheet 6 Filed Sept. 7, 1950 /NVENTOR.Jasep/IE' 0y 5v Arronuzv United States Patent Dam.

Joseph F. Joy, Pittsburgh, Pa., assignor to Joy Manufacturing Company,Pittsburgh, Pa., a corporation of Pennsylvania Application September 7,1950, Serial No. 183,585

Claims. (Cl. 255- 37) This invention relates to a combination wrench anddrill device, especially to a portable device for use in mines. 7

There are many requirements in underground mining today for drilledholes. One such application is connected with the relatively newpractice of roof bolting as a substitute for timbering to prevent rooffalls. This method of roof control is disclosed in my application Ser.No. 120,734, filed October 11, 1949, and necessitates drilling holesinto the mine walls, locating an expansion bolt in each hole thus made,and bolting a plate, angle iron, channel, or the like tightly againstthe strata by means of the expansion bolt. The strata are thus held to aminimum of flexing and roof falls are effectively prevented.

With this method of roof control, it often happens that the hole whichis to be drilled must be substantially longer than the dimension of thespace in which the work must be done. There is, accordingly, a real needfor a light, mobile drill, capable of standing erect, and of drilling ahole into the strata which is greater in depth than the height of thespace in which the drill is located. There is moreover, a need for atool which can quickly tighten up the nuts on the bolts in order toavoid the time-consuming tightening of these nuts by hand. It may benoted, however, that the need is not limited to holes in the roof, andthe device of this invention is capable of general application todrilling in underground mines.

It is, accordingly, an object of this invention to provide an improveddevice which carries a drilling tool and which is telescopically mountedand is extensible to a length greater than the drill height; it is afurther object of this invention to provide such a device which iscapable of engaging and tightening the nuts on the roof bolts. Otherobjects and advantages will be apparent 7 to those skilled in the art.

In the drawings:

Fig. 1 is a view in elevation of the device as seen from the cable reelside.

Fig. 2 is a top plan view of the device.

Fig. 3 is a view in section substantially on line 3-3 of Fig. 2. 1

Fig. 4 is a view in section substantially on line 4-4 of Fig. 3, but ona larger scale.

Fig. 5 is a view in section substantially on line 5-5 of Fig. 3.

Fig. 6 is an enlarged detailed sectional view through the rotatableshaft which carries the drilling tool. This figure is a section onsubstantially the same plane as that of Fig. 3, but on a larger scale,and is limited to the hydraulic cylinder details and parts immediatelyadjacent thereto.

Fig. 7 is a top plan view of just the end of the extensible drive meansshowing the wrench in place.

Fig. 8 is a side elevation view of those parts of the device shown inFig. 7.

Fig. 9 is a view in section substantially on line 9-9 of Fig. 3, but ona larger scale.

Fig. 10 is a view in section substantially on line 1010 of Fig. 6, buton a larger scale.

Fig. 11 is a schematic diagram of the hydraulic system which isconnected to supply power to extend the telescopic drive means. Theapparatus is shown in Fig. 11 in its neutral position-i. e., in theposition in which fluid is trapped in the hydraulic cylinder.

Fig. 12 is a view similar to Fig. 11, but showing the valve in theoperating position in which fluid is supplied to the hydraulic cylinderto extend the telescopic drive means.

Fig. 13 is a view similar to Fig. 11, but showing the valve in positionto allow fluid to be withdrawn from the hydraulic cylinder.

Fig. 14 is an operational side elevation view showing the device in anerect position placed between the floor and the roof and drilling a holein the roof.

Fig. 15 is a similar operational view, but showing the device located todrill a hole in the roof at an angle from the vertical, and

Fig. 16 is a partial view in elevation of the extensible drive means,but showing the wrench in place and in engagement with a nut on the endof a roof bolt.

Referring now to the drawings in detail, a device made according to thisinvention is shown as having a support such as a housing 2 provided witha bottom plate 4 removably secured to the housing by means of bolts 6,anda cover 8 removably secured to the top of the housing by means ofbolts 10.

The device is preferably made mobile by providing a pair of rubber-tiredwheels 12 suitably mounted on the housing. The wheels 12, of course,constitute a floor-engaging support by which the device is readily movedabout from job to job. A second floor-engaging support 14 is suitablysecured to the bottom plate 4. The support 14 in the preferredembodiment consists of a beam having downturned ground points 16 at itsends, and being pivotally secured at a point between its ends to thebottom plate 4 by means of a bracket 18 and a pin 20.

The cover 8 supports a pair of tubular columns 22 and 24 by means offlanges 26 secured to the lower ends of tubes 22 and 24; the flanges inturn are secured to the. cover 8 by any suitable fastening means such asthe bolts 23. Rods 3i have telescoping engagement with the tubes 22 and24, and are clamped in any desired position by means of the knurled nuts32 which have threaded engagement with the split upper ends of tubes 22and 24. .Handle bars 34 are secured to the upper ends of rods 30, andare connected by a central ring 36. A leg 38 having a curved foot 49 issecured to the ring 36 by means of a pair of brackets 42. Hand grips 44are provided at the outer extremities of the handle bars 34.

A drilling tool 46 of any suitable type is extensibly carried and drivenby a hydraulic cylinder 48 (Figs. 3, 6, and 10). Hydraulic cylinder 48is rotatably carried in a hollow support 50 which is preferably anintegral 7 part of the main housing 2. Hydraulic cylinder 48 is.-rotatably mounted in bearings such as the anti-friction bearings showngenerally at 52 and 54. As is best evident in Figs. 3 and 6, cylinder 48is held against axial movement by the same anti-friction bearings 52 and54.

Near its lower end, cylinder 48 is fitted with keys 56. A shipper ring5% has sliding engagement with the keys 56, and carries internal teethand 62 at its opposite ends. The ring 58 is grooved between its ends asshown at 64, the groove 64 being adapted to receive the pins 66 of ashipper yoke 68.

The internal teeth 60 and 62 of the shipper ring 58 comprise a dogclutch engageable alternatively with external gear teeth "70 and 72,respectively. The shifting of the shipper ring 58 by means of shipperyoke 68' is accomplished by an operating handle 74 (Fig. 2) which may beconnected in anysuitable manner, aswill be, understood by thoseskilledin the art, to manipulate the yoke 6,3.

byany suitable bearing means, and carries secured thereto a gear 126which meshes with another gear 128. Gears 126 and 128, together with thecasing 124, constitute a gear pump 130. Gear pumps of this type are wellknown in the art and need not be detailed here.

Gear pump 130 provides fluid under pressure for'the hydraulic systemthat includes the hydraulic cylinder 48 and a valve 132. It will beunderstood that this hydraulic 1 system uses the well 134 in bottomplate 4 at one side of artthat the showing of the motors is incomplete;for the sake of: simplicity', the motor field windings and the brusheswhich contact the commutators 86, are. notshown,

Itwill be understood that the motors are, substantifilly identical inorder that the parts thereof may be interchangeable. The rotor shaftsextendjdownward as shown at 88 and 89. and carry near their lower endsdrive pinions 90 and91'. The pinions mesh with andfdrivealarge gear 92-see alsoFi'g. 5). Large gear 92 is provided with an integral hub 94 onwhich are, formed the gear teeth 70' referredto aboveas'being'engageable with the internal teeth ofjthe shipper ring'58: Seealso Fig, 6;, The

' teeth extend substantially the. full length f the,- hub 94,-andengageattheir upper endsa pair of gears 9 6jand 98: The gear961 iskeyed to anddrives a shaft 10Uwhi'ch is rotatable in-anti frictionbearings 102 and 104; Shaft is provided at its lower end with externalteeth 16,

forming-adrivepinion which meshes with a centrally located gear 108rotatable on a sleeve bearing 1109 on the hydraulic cylindersr Gear 108'is provided with a centraLhub-1-la0on which are formed the gear teeth orsplines, 72; referred to above as being engage'able with the internalteeth or splines 62 of" shipper ring 58.-

Gear: 108 desirably-incorporates" a clutch having a disclllaintegralwith the gear teeth and" gripped between discsl Ll-b and111a; Springs 112 provide the pressure to achieve the necessary frictionbetween discs;

Similarly; gear-98iskeyed to a hollow shaft'113'which is-rotatableinantifr-iction bearings'1e14 and 116; Shaft 113 carries an integralpinion 118 which corresponds to the=pini0n 106; and whichalso mesheswith the large centrally located gear 1 0%.

From the: foregoing, it will be evident to those skilled" in. theartthat the. external gear'teeth 79 are driven by theelectricmotors at agiven speed; and thatthe drive fonthesexternal gear teeth-72 is at asubstantially reduced" speedz A; desirable speed of the teeth 70 is 5-20R P Mi, toednivelt-he drilling tool: 46; and adesirable speed of the;teeth 72is. 5931 R R M., to drive the wrench (latende scribeds); Thusthe gears having teeth 70 and 72 00111- pi'ise a-plurality ofdrivenmembers connected to the elec: tricmojtop onmotors, and shipper-ring 5Sis-a drive mem-' bar; the-islcn'ppenfork and handle 74, together withtheir connecting linkage ete.,. form means toconnect-r aselected oneofgthe;driveremernbers 70; and 7-2 with'thedrive memberaistto driveoneofsaid: driven members. 1

ever; in this instance, a shaft 1-20 extends through thehollowshaft-113; and is-provided with a tongue ar its uppenend; to engagethenotched lower end ofextension 8Sb Shaft 120-is thus drivenbyrotor-78; Anits-lower; end, shaft 120 is rotatably mountedina gear:casing 124 the machine as a sump. The valve body or cylinder 136 isprovided with a flange 138 at its upper end; whichis bolted to aseptum'in the lower part of housing 2; thus completing an enclosedchamber 139 for the valve'132. The chamber 139 and the correspondingspaeein the other side of the casing are filled with oil and serve as arescrvoir. The valve cylinder or-body- 1 363is open at its lower end tothe sump 134. Reciprocable within the valve body or cylinder 136 is avalve member 141 in the shape of a o l .90 1. h v n an. ppe a d. 142and; a L w r. lan 143,..with a, groove betweentthem, Theuppenland, 1 42:is provided with diagonal passages144 communicating with, the hollow of;the spool. At itsnpper end, the spool carries an, extension 145 which isgroovedtorecei-ve. the actuating; pin of a shipper arm 146. The. shipperarm lj idfis connected in a,'suitable manner to be; actuated from theexterior of, the housing byan, operating handle 1:47. (Fig, 2 aswillbe-well'understood by those skilledin the,

Con uit. 1, c nnec s. h upper nd of cylind 3 with thqp ump suction, anda. conduit 149 (Figs, 11,12 and 13) connects thepump dischargewiththelowen end. ofcylipde 136 by way of passage 150; A conduit 151connects valve 132 with the lower end of hydraulic cylinr der 48, by wayof a radial passage 152, in. cylinder head 5: n an ax allpassag .5 e eing upward rom. he: radialjpassage 152. A pressure reliefvalvevrislocated. in a branch offconduit 149, anddischargesinto thereservoirspace. Obviously, valve, V; is effective, (andnecessary) only for theoperating position of member 14L shown in Fig; 112.

As is best seen in Fig, 6, axial passage 15,6; opens into; the lowerinterior of cylinder 48;- Slidable axiallywithin cylinder'48l is anannular member 158,. Annular member- 158 is preferably provided'at itslower end, with any suit,-

Y able seal;- such as the O-ring shown lyingin the groove (Fig: 6).Annular member 158 is provid'edwith keywaysi a resilient annular ring;of any suitable substance 7 such as rubber or the like. A second shortdepending skirt 172 forms with the skirt 164'an annular grooye whichreceives a suitable packing material 114., The

paching' 'lTdis-engaged by the upper endof asleeve 176 which is providedwith a flange 178'whereby it'is, secured by means ofbolts180to-thecover-8i A- second annular-'member1-8 2', similar to butsmaller than annular member 158, is reciprocable inside-the eunularmeniber' 158; The two annular'members158 and 182 are keyed togetheragainst" relative rotation by'meansofi keyway s 184 provided in theouter surface or member 182, and keys 186 (shown in dotted lines in Fig.10), carried' in annular rnember- 1-58 initsupperend". v A sec ond uppencyli'nder head- 188 is screwed to theupper end of annularmember .158 at190.- Upper cylinderhead 188 has no depending skirt tohold the keys 186in place inannular member-158 in the manner that upper cylih der head166 holds the keys 162 in place in Cy inder4i Instead; keys 186' merelyfit through 'slots' (not shqwn) in member 158; and are preferablyweldedin place.

Annular member ls fi' has securedtoits-upper end192 a.

sleeve 194, slotted as shown at 196 to discharge the cuttings; sleeve194 is provided with an internal flange 198 at its lower end. Flange 192is welded as shown at 200 to the annular member 158 at the upper end192. Upper cylinder head 188 is screwed to the upper end of annularmember 158, as indicated above, and bears against the upper face offlange 193. At the lower end of its interior, annular member 158 isgrooved to receive a snap ring 202. The snap ring 2il2 serves as a lowerlimit stop for the annular member 182.

A third annular member 204 is reciprocable or slidable telescopicallywithin the annular member 182, and is secured against rotation relativethereto by means of keyways 206 in annular member 204 and keys 208secured in slots in annular member 132 and held in those slots againstradially outward movement by the keeper strips 210 which may be securedin place in any suitable manner. A third upper cylinder head 212 isthreaded to the upper end of annular member 132. At the lower end of itsinterior, the annular member 182 is grooved to receive a snap ring 214which serves as a lower limit stop for the annular member 204.

As in the case of the annular members 158 and 182, the annular member2th; is provided at its lower end with a pistonlike portion which is notcut by the keyways 206, and which carries an O-ring to provide a fluidseal.

A shaft 216 is telescopically mounted with respect to the annular member2 34 and is held against rotation with respect thereto by means ofkeyways 218 in the shaft and keys 22d and 221 secured in the annularmember 29 5 near its upper end. Keys 220 and 221 may be secured in placein any suitable manner, as by being inserted through slots in the wallof the annular member 253 and welded in place.

A fourth upper cylinder head 222 is threaded to the upper end of annularmember 204. Near the lower end of its interior, annular member 294 isgrooved to receive a snap ring 224. Snap ring 224 serves as a lowerlimit stop for the rotatable shaft 216.

Cylinder heads 188, 212, and 222 are provided with seals or annularrings of rubber or the like, similar to the annular ring 170 providedfor cylinder head 166. It will be understood that the rubber seals willhave radially inward projecting ribs filling in the keyways to keepforeign matter out of the mechanism.

The sleeve 124 carries at its upper end a device 226 to engage anextraneous abutment, as for example the roof of a mine room. Inasmuch asthe abutment engag ing device 226 will be stationary with respect to theabutment it engages, it must be rotatable with respect to the annularmember 153 on which it is carried by means of the sleeve 194-. Thisrelative rotation is provided by the antifriction bearing 22%. Device226 may be, and preferably is, provided with serrations 230 at its upperend.

Sleeve 194 is provided with openings to receive pins or dogs 232-. Dogs232 extend radially inward beyond the inner surface of sleeve 1% andserve to engage slots 234 of a'tool such as a wrench 236. The wrenchattachment 235 is provided with a suitably designed central opening 238(Fig. 7) adapted to lit the nuts that are to be screwed to the ends ofthe expansion bolts.

Reference is made again to the electric motors which drive the gear pumpand the hydraulic cylinder. The rotors 76 and 78 of these motors areshown as provided with cooling fans 240 at their lower ends. Suitableaxial passages will be provided through the field windings (not shown)to allow the passage of cooling air through these windings. Other axialpassages 241a (Fig. 4) and 24117 are provided in the outer portion ofthe casing 2. Brush supports in the form of discs 242 are securedadjacent e commutators or the rotors by being clamped between the upperends of the motor housings 244 and depending skirts 246 of cover 3. Asis best seen in Fig. 9, discs 242 are provided with peripheral recesses248 to permit the passage of the cooling air into the field windingsfrom the end spaces 250 provided by the cover 8. The skirts 246 areslotted as shown at 252.

Power is supplied to the electric motors in any suitable manner, as forexample through a power cable 264 carried on a cable reel 266. Suitableswitch means housed in a box 268 and having an operating button 270 isprovided in order to allow the power circuit to the motors to be madeand interrupted at will.

Operation In the use of a device made according to this invention, thedevice is wheeled about in the room to the location where it is desiredto drill a hole, as taught in my aboveidentified application Ser. No.120,734, filed October 11, 1949. By way of illustration, it will beassumed that a hole is to be drilled in the roof. The machine is upendedon the ground-engaging support 14 into the position shown in Figs. 3 and14, or Fig. 15, whereupon the operator manipulates the handle 74 toengage the shipper ring 53 with the gear teeth 70 or the gear teeth 72,depending on the operation. In this case, it is assumed that a hole fora roof bolt is to be drilled, so the ring 53 will be shifted upward inorder to make the connection for high speed. The electric power switchis then closed by pressing button 274 to complete a circuit to themotors. With the motors operating, the gear pump 130 is rotating and issupplying oil under pressure to the valve 132 by way of conduit 149.

With the valve in the position shown in Fig. 11, oil merely circulatesthrough the center of the hollow spool. The operator moves the handle147 to shift the valve member from the position shown in Fig. 11 to theposition shown in Fig. 12. Oil under pressure is then supplied from thepump to the bottom of the hydraulic cylinder 48.

With oil under pressure supplied to the lower end of cylinder 43,annular members 158, 182, and 204, and shaft 216 all move upwardtogether, until the roof-engaging device 226 brings its serrations 230into contact with the roof. There may be some slight penetration of theroof by the roof-engaging device (but such penetration will be largelysuperficial) until substantial resistance is ofiered by theroof,whereupon the drill presents a substantially rigid column extending fromthe mine bottom to the roof by way of the telescopic hydraulic cylinderand annular member 158.

It will be remembered that meanwhile the two motors are rotating thehydraulic cylinder, the annular members and the rotatable rod by meansof pinions and 91, gear 92, gear teeth 7%, internal gear teeth 60,shipper ring 53 and keys S6, 162, 186, 208, 220 and 221. This" is thehigh-speed drive and the drill- 46 rotates at drilling speed.

As soon as the roof-engaging device 226 encounters substantialresistance and stops its upward movement, the next annular member 182moves telescopically outward and upward from the annular member 158. Thedrill cuts into the roof strata and the cuttings drop downward and fallout through slots 196. Annular member 182 continues to movetelescopically outward, sliding axially within annular member 158, untilthe ends of keyways 184 come against the lower ends of keys 186. Whenthis limit of travel of the annular member 182 is reached, annularmember 204 slides within annular member 182 until the lower ends ofkeyways 206 come against the lower ends of keys 208.

When the upper limit of travel of annular member 204 is reached, shaftor rod 216, which now acts as a piston the hydraulic cylinder, movestelescopically upward,

advancing the drill into the roof. Rod 216 moves upward within annularmember 204 until the ends of keyways 218 come against the lower ends ofkeys 220. This represents the absolute upper limit of travel of thedrill,

, but it will be observed that the drill is now extended. 7

upward from the position shown in Figs. 3 and 6 by subnti llv h l ngth.of. nn l r members. 182 nd.;2.Q4,, androtatabl'e' rod Zld, pluss'uchupwarcfmovementofi annular member 158' as was possible.untiLroofi-engaging device, 226 .came into contact with the roof; minus,of course, .the limitations imposed by the fact that the severalikeywaysmust of necessity remain in engagement with their respective keys.

It may be noted that reliefivalve Vr may be by-passiug oil some of thetime during upward movement of the drill. Valve VT will be setto open ata pressure high enough to give anadequately high pressure to advanceshaft 21-6 alone against the resistance oftheroof strata. Ifi the drill:should move upward so fastas to overload the drill drive motors, theoperatorcan slowdown thefeed by-manipulatingvalve member 141' so as tothrottle thefluid going to cylinder 43.

Itwillt be observed' that: thedrill= bit cuts an opening larger than theoutside diameter ofthelargest cylinder entering the drilledhole-namely-, the annular memberlower the drill and itsconnectingrotating rod and annular-members; the operator manipulates thehandlehandle. 141 to shift thevalve-member from the position it occupiesin Fig. 13v into the position shown in Fig; II, in. which position fluidis trapped in cylind'er' 48, and the downward movement of the drill isarrested; if it has not; already reached the extreme lower limit oftravel. The. operator.- manipulates handle 74- to shift the shipper ring58 into neutral, and then slips the wrench attachmerit: 236. into placewith, the slots 234 engaging the pins: 232.

A.roo boltis put into place and secured in the hole justamadeby. thedrill; Roof bolts of any suitable type may'be used, such as the boltsdisclosed and claimed in; my copending. application Ser. No. 120,734,filed October. 11,. 1949;. referred: to above. A. crossbeam orplatea2i2imay then be placed againstthe roof and' anut: started:manually on the projecting end ofthe bolt; if the: hole. is; at; anangleas. in Fig. 16, an angle iron 274 may be added, after which theoperator; manipulates the handle 14.7: tmadmit: oil: under pressure tothe bottom of therhydraulie' cylinder 48, moving annular member 158' fupward luntillltheawrench engages plate 272 or angle274),

zit-which; time thezopenir g 238 in the wrenchattachmentisiin position;to receive; the. nut; The operator then manipulates the. handle; 147to'trap the oil within cylinder 48 to hold the wrench in the desiredposition. The. shipper-ring 58;. is then shifted tomesh teeth 62 and 72,

rotatiugthe wrench at; lowspeed, whereupon the nut is screwedup tight'iby power. of theelectricmotors to clamp the, plate;272. firmlyagainstthe roof: When thenut: is-tight; thev clutchdiscs 1112:: and 111:: stop,and

V disq: 1:11. 11 Slips. between them.

The bove. description of operation of adevice made accojfiiilg to: this,inventionhas concerned its application tothe taslgofj drilling athol'ein: thereof, securinga bolt 111 1325 l lt h tt file, andrtightening. anuton the bolt.

It vwill ofgcourse be. evident tothoseskill'ed'inthe-art that As will beunderstood by those skilledinthe art; a deviceqmade according-to thisinyention" can also housed tor-remove-nuts ftomroof bolts, merely byreversing the drive motors: Other'uses'will become evident to thoseskilledeiirthe art. V

, mounted in theanuular member, means drivingly engagingthe annular,member. and the piston, means to mount.

nevencontami'nated with dust from the mine atmosphere.

The specific air cooling means shown here forms no part of thisinvention. 7

It will be evident to those skilled in the art that this inventionprovides an easily movable power-operated drill" and wrench which willWork in a space of low vertical height and which can drill holes equalin length to several times the vertical height of'the workingspace orroom; and that thisinvention provides a further advantage in embodyingin. one machine a drill as well as a power operated wrench. Otheradvantages will be apparent'to those skilled in the art.

While there is in this application specifically described one form whichthe invention may assume in practice, it will be understood that thisform of the same is shown for purposes of illustration, and that theinvention may bemodified' and embodied in various other forms withoutdeparting from its spirit or the scope of the appended claims.

I claim: 7

l". A drill; comprisinga floor-engaging support, a fluid pressurecylinder rotatably carried by the support, an annular member havingtelescopic engagement with the cylinder and beingextensible uponadmission of fluid to the cylinder, a roof engagiug member, means tomount the roof-engaging member on the annular member for free, rotationrelative. thereto, a piston rcciprocably mounted in the annular memberand having means for fixing it against rotation, relative to thecylinder, means tomgunt a d'rilling tool onthe piston for axialmovement.

ber,, means. for, rotatably, mounting said roof engaging member onjtheannular member, a piston reciprocably.

a drilling toolonthe. piston for; axial movement and for. rotation bythe.piston,.means,to supply iluid under pres- V surelto the. cylinderandto withdraw fluid from the cyl inder,. and. means: to. rotate thecylinder.

3,. A, drill, as in claim. 1 in which. the roof-engaging memberis,annular,,and.lias a plurality of, closelyspaced serrations onv themember in position to engage a roof. 4:1A. drill as in claim- 3, inwhich the annular race.

engaging member; is provided with abore and themeans.

5. A drillas-in claim 1, in which the twolast-named means includeacommon drive motor.

6; A drillk as in claim l, in which the roof-engaging, meniberisprovideti'witli a. bore andthe means'to mount the roof engaging memberon the annular member in 8: In a drill-as in claim 2, a pluralityoicloscly spaced,

serrations: on the roof-engaging member, in. engagethe roof.

9. A drill. as, in claim, 2, in which theroofiengaging,

position to References Cited in the file of this patent UNITED STATESPATENTS 2,007,666 Smith July 9, 1935 10 Holmes July 19, 1938 Gardner,Jr. Apr. 9, 1940 Suzuki Dec. 10, 1940 Osgood Jan. 6, 1942 Possum Oct. 5,1943 Karweit Apr. 15, 1947 Allen Apr. 14, 1953

